A lunar month in pregnancy is four weeks or 28 days, meaning that pregnancy lasts ten months rather than the conventional concept of nine. According to Baby2see.com, some world health organizations, in an attempt to standardize pregnancy calendars, tried unsuccessfully to get the lunar month method adopted universally.
The lunar month pregnancy actually begins on the first day of a woman's last menstrual period. Although she likely does not become pregnant for another two weeks, four weeks from that day she is said to be four weeks into the forty week pregnancy process. By this method, a pregnancy is 280 days long. In many places, this method is the traditional one for tracking pregnancy.